Up to 10% of all surgical patients experience wound complications which result in increased hospital costs and lost productivity amounting to more than a billion dollars per year. Yet no objective method exists for noninvasively evaluating factors affecting the repair process such as: diabetes, low oxygen tension, infection, systemic steroids, genetically engineered growth factors, suture material or cytotoxic drugs. Initial studies have shown that high frequency ultrasound is a promising modality well-suited for making such noninvasive measurements in humans. The long term goal of this work is to develop acoustic methods capable of making objective noninvasive clinical measurements of material properties for surgical wounds. In addition, results of this work will provide basic knowledge regarding the interaction of ultrasonic energy with soft tissues, which is essential for the development of tissue characterization techniques applicable to a wide range of connective tissues. Important acoustic parameters will be investigated using a well characterized wound model. A highly quantitative scanning laser acoustic microscope (SLAM) will be utilized at 10, 30, and 100 MHz to characterize basic acoustic properties of wounds in vitro. Backscatter acoustic techniques (BAT), which are directly applicable to the clinical environment will be utilized at 10-40 MHz for in vitro measurements. Early wounds (1-21 days) will be studied since they are of great interest clinically and our work to date indicates that the greatest change in acoustic behavior is expected during that time period. Changes in attenuation coefficient as measured with BAT are expected to provide insight for clinical measurement procedures for eventual in vivo evaluation of repair. Older wounds (50-365 days), where the principal change in collagen is the three dimensional architecture, will also be studied. Acoustic measures of structural size distribution (heterogeneity index and frequency dependent backscatter) will be correlated with changes in fiber bundle size. Additionally, we will utilize specially prepared biological specimens (collagen gel and articular cartilage models) to isolate the important contribution of cross-linking and proteoglycans to the acoustical properties of the healing wound. Development of ultrasound techniques capable of measuring material properties in wound tissue should provide a clinically relevant method for evaluating human wounds objectively and in a noninvasive manner.